As an important translation technique, part of speech translation is significant for all translators. In the study of part of speech translation ,Eugene Nida ,a famous American translation theorist, who has created a new classification system ,which is the most representative theory whose core concept is "functional equivalence" and applied to translation practice . From the perspective of linguistics Eugene Nida put forward the famous translation theory "dynamic equivalence" according to the essence of translation. In this theory, he pointed out that translation is to reproduce information group of the source language from semantics to style of the text by the means of the most appropriate and nature equivalent language.(176)

The linguistic equivalence including the equivalence of sound, morpheme, word, phrase, sentence and discourse and so on. At the same time, equivalence in translation is a comprehensive relationship, not only including semantic equivalence but also stylistic and style equivalence included .People in the same society must abide by the same language classification standard, otherwise, it is impossible to communicate, while people in different social and cultural, language classification system will naturally be different, this is the salient features of different languages. Some  thoughts of equality relation in our minds ,taking  “A” in English equals to “甲” in Chinese for example , are mostly illusion, is not consistent with the actual situation .Between English and Chinese not only lexical semantics of two languages are not completely corresponding to each other but also parts of speech are also not corresponding. Therefore, in English-Chinese translation, in order to make the readers get the same feelings with original readers ，language translation must be changed to obtain constant content and effect. However, giving up the form not means to neglect the meaning expressed by the forms of discrimination, but to completely and accurately convey the original information on the basis of full understanding to the function and to flexibly convert some parts of speech in the resource language to some certain corresponding parts of speech in target language at the premise of accurate reproduction of the original information.

It is necessary to research on the principles and Strategies of lexical category conversion, so as to explore how people understand in the practice of translation and the translation techniques using speech conversion. Study of part of speech conversion in English-Chinese translation practice is conducive to improve the skills of translation practice, make the expression of translation text more picturesque and vivid and the version more fluent.